Thank you, but the keycap is made of plastic , not aluminum and has already fallen off. So i think I just need to find a new keycap. The mechanism on the seating end of the keycap looks a bit complex, but I hope pressuring it into place will work.

Even a slightly-marring tool helped me, a small flathead screwdriver for lifting up the top part of the H- and J-key, until I got a better grip with just my fingers - wiggle, and pop! The key cap came off. (I got my hands of a wireless keyboard where the H and J keys were switched, for some crazy reason) and now it workes like a charm. I just popped the caps back onto the two keybases again, "k-pop, k-pop". Lovely.